Enhancing electrochemical and electrochromic performances of carbazole comprising monomer via copolymerization with 3,4-ethylenedioxythiophene (EDOT)

Abstract

In this study, two novel electrochromic copolymers (CoP1.3 and CoP1.5) were synthesized via electrochemical methods and characterized. The comonomers used in the synthesis were 3,4-ethylenedioxythiophene (EDOT) and a carbazole comprising monomer; 9-(2-(4-(Phenyldiazenyl) phenoxy) ethyl)-3,6-di(thiophen-2-yl)-9H-carbazole (M1). Carbazole containing monomer (M1) and EDOT were combined with two different comonomer feed ratios, 1: 3 and 1: 5 respectively in order to investigate the effect of increasing EDOT amount on electrochemical, spectroelectrochemical and electrochromic behaviors. The electrochemical and spectroelectrochemical characterizations of the electrochemically obtained copolymers were performed by cyclic voltammetry (CV) and UV-vis-NIR spectrophotometry. Both copolymers exhibited p-type doping with reversible oxidation potentials reported at 0.23 V/0.93 V for CoP1.3 and 0.30 V/0.98 V for CoP1.5. The difference between these oxidation potentials could be dedicated to the difference in electron density in the copolymer chains. Optical band gap values were calculated from neutral state absorptions as 1.21 eV and 1.18 eV for CoP1.3 and CoP1.5, respectively. Due to the higher EDOT amount in the copolymer backbone, the band gap for CoP1.5 is lower than that of CoP1.3. Both CoP1.3 and CoP1.5 exhibited multichromic behavior with different colors in the neutral and oxidized states. While both copolymers (CoP1.3 and CoP1.5) exhibited purple color in the neutral states, the colors turned to blue colors upon applied potentials. Optical contrast values were calculated as 31 % (at 555 nm), 55 % (at 1050 nm) and 38 % (at 1240 nm) for CoP1.3 and 34 % (at 565 nm), 25 % (at 975 nm) and 45 % (at 1170 nm) for CoP1.5. As a result of electrochromic switching studies, switching times (oxidation) were calculated as 2.5 s, 1.7 s, 1.9 s for CoP1.3 and 1.9 s, 1.8 s, 2.7 s for CoP1.5. Furthermore, addition of EDOT unit into copolymer backbone resulted in the obvious improvements in electrochemical, optical, electrochromic and kinetic properties. Copolymers exhibited full visible absorption with red-shifted neutral state absorption, lower optical band gap values compared to those of homopolymers.